The invention relates to a method of forming a cylindrical member, in particular, a method of forming a cylindrical member having a highly close dimensional accuracy with a press operation alone without requiring a subsequent processing technique.
A conventional technique to form a cylindrical member such as a bush by a press operation starts with a web material which is cut into strip material of a given length. Only the opposite ends of the strip material are bent into a radius of curvature which is slightly greater than the radius of curvature of a cylindrical member which is intended to be manufactured. Subsequently, the strip is bent into a U-configuration by a bending process, and then placed between a pair of dies which are used in a coining step for forming the U-shaped material into the configuration of cylindrical bearing surfaces which are formed on the pair of dies. The described technique provides a cylindrical member having a favorable configuration when viewed macroscopically. However, when a high level of circularity is required of the products such as bushes, the press operation alone is insufficient to achieve the required accuracy. In particular, the level of circularity of the product in the region of its abutting ends is distinctly degraded in practice as compared with such level of the remaining regions. Consequently, the conventional process of forming a bush required a subsequent processing such as trimming or grinding operation after the bush is formed by a press operation. Hence, it is obvious that there have been a need in the prior art for a technique which improves the machining accuracy and reduces the machining cost.